When a technical problem occurs in a passenger transportation system, the elevator car of an elevator, for example, must be halted as quickly as possible. Such a process, known as an emergency stop, is effected by the immediate triggering of a service brake of the passenger transportation system. Further, in known passenger transportation systems of the prior art, on occurrence of an emergency stop, a drive motor of the drive machine is simultaneously disconnected from the electricity network. For a user of the passenger transportation system, emergency stops are very unpleasant, because, in order to achieve as short a braking distance as possible, the braking power of the service brake, and the resulting braking deceleration, are very high. Mechanically, an emergency stop can only be controlled with difficulty, since the braking deceleration depends to a great extent on the kinetic energy that must be braked, the condition of the service brake, and the temperature of its brake linings. This can cause forces on the user that exceed 1 g.
From EP 1 997 765 A1 a brake control for an elevator car is known. By means of this brake control, the braking force of an electromagnetic brake at the instant of an emergency stop can be so controlled that the braking deceleration of an elevator car matches a predefined value. This is based on a deceleration control value and a velocity signal. However, it is regarded as a disadvantage that the calculations that are required for this purpose take a long time, which delays the generation of the braking force. For this reason, the brake control that is known from EP 1 997 765 A1 has an embodiment in which a portion of the total braking force that is generated at the instant of the emergency braking of the elevator car can be adjusted. Further, a non-adjustable portion of the braking force is foreseen, which generates a braking force immediately, without an adjustment of this portion taking place at the instant of the emergency braking of the elevator car.
The brake control that is known from EP 1 997 765 A1 has the disadvantage that, although a reduction of the braking force during braking of the elevator car is possible, and at the same time a more rapid commencement of the braking effect with the non-adjustable portion of the braking force occurs, system-related delays on switchover nonetheless worsen the braking behavior. Further, the predefined non-adjustable portion of the braking effect is only not too large if it is predefined correspondingly small. Such a low predefinition of the braking effect can have the effect that, in most cases, on initiation of the emergency braking, the braking effect is too little.
A braking method for a passenger transportation system is also disclosed in U.S. Pat. No. 6,896,119 B2. This braking method comprises the method steps that, as well as an activation of the service brake, also the disconnection of the drive machine from the power-supply network is triggered. According to this braking method, the disconnection of the drive machine from the power supply network, by switching off the frequency converter, only takes place after the service brake has been activated. This braking method has the disadvantage that, although the disconnection of the drive from the power-supply network takes place after the activation of the mechanical service brake, the braking effect of the mechanical service brake remains completely disregarded.